Hoek J B, Taraschi T F, Higashi K, Rubin E, Thomas A P
Department of Pathology and Cell Biology, Thomas Jefferson University, Philadelphia, PA 19107.
Biochem J. 1990 Nov 15;272(1):59-64. doi: 10.1042/bj2720059.
The activation of phosphoinositide-specific phospholipase C by ethanol was compared in hepatocytes isolated from ethanol-fed rats and from pair-fed control animals. Ethanol (100-300 mM) caused a dose-dependent transient increase in cytosolic free Ca2+ levels in indo-1-loaded hepatocytes from both groups of animals. The rate of Ca2+ increase was similar in hepatocytes from control and ethanol-fed rats, but the decay of the Ca2+ increase was somewhat slower in the latter preparation. The ethanol-induced Ca2+ increase caused activation of glycogen phosphorylase, with 50% response at 50 mM-ethanol and a maximal response at 150-200 mM-ethanol, not significantly different in hepatocytes from control and ethanol-fed animals. Ins(1,4,5)P3 formation in response to ethanol (300 mM) or vasopressin (2 nM or 40 nM) was also similar in the two preparations. It is concluded that long-term ethanol feeding does not lead to an adaptive response with respect to the ethanol-induced phospholipase C activation in rat hepatocytes. The ability of ethanol in vitro to decrease membrane molecular order in liver plasma membranes from ethanol-fed and control rats was measured by e.s.r. Membranes from ethanol-fed animals had a significantly lower baseline order parameter compared with control preparations (0.313 and 0.327 respectively), indicative of decreased membrane molecular order. Addition of 100 mM-ethanol significantly decreased the order parameter in control preparations by 2.1%, but had no effect on the order parameter of plasma membranes from ethanol-fed rats, indicating that the plasma membranes had developed tolerance to ethanol, similar to other membranes in the liver. Thus the membrane structural changes associated with this membrane tolerance do not modify the ethanol-induced activation of phospholipase C. The transient activation of phospholipase C by ethanol in hepatocytes may play a role in maintaining an adaptive phenotype in rat liver.
对乙醇喂养大鼠和配对喂养对照动物分离出的肝细胞中乙醇对磷酸肌醇特异性磷脂酶C的激活作用进行了比较。乙醇（100 - 300 mM）使两组动物经indo - 1负载的肝细胞中胞质游离Ca2+水平呈剂量依赖性短暂升高。对照组和乙醇喂养大鼠的肝细胞中Ca2+升高速率相似，但后者制剂中Ca2+升高的衰减稍慢。乙醇诱导的Ca2+升高导致糖原磷酸化酶激活，在50 mM乙醇时出现50%反应，在150 - 200 mM乙醇时出现最大反应，对照组和乙醇喂养动物的肝细胞中无显著差异。两种制剂中，对乙醇（300 mM）或血管加压素（2 nM或40 nM）反应产生的肌醇（1,4,5）三磷酸形成也相似。得出的结论是，长期乙醇喂养不会导致大鼠肝细胞对乙醇诱导的磷脂酶C激活产生适应性反应。通过电子自旋共振测量了体外乙醇降低乙醇喂养大鼠和对照大鼠肝细胞膜分子有序性的能力。与对照制剂相比，乙醇喂养动物的膜基线有序参数显著更低（分别为0.313和0.327），表明膜分子有序性降低。添加100 mM乙醇使对照制剂中的有序参数显著降低2.1%，但对乙醇喂养大鼠的质膜有序参数无影响，表明质膜已对乙醇产生耐受性，类似于肝脏中的其他膜。因此，与这种膜耐受性相关的膜结构变化并未改变乙醇诱导的磷脂酶C激活。乙醇在肝细胞中对磷脂酶C的短暂激活可能在维持大鼠肝脏的适应性表型中起作用。
